Process of chrome tanning



UNITED STATES FRIEDRICH HIRSCH, 0F VIENNA, AUSTRIA.

PROCESS OF CHROME TANNING.

Specification of Letters Patent.

" Patented J an. 31, 1922.

No Drawing. Application filed March 5, 1914, Serial No. 822,696. Renewed January 29, 1918. Serial No. 214,415.

(GRANTED UNDER THE PROVISIONS OF THE ACT OF MARCH 3, 1921, 41 STAT. In, 1313.)

To all whom it may concern Be it known that I, FRIEDRICH Hmsorr, a subject of the Emperor of Austria, and a resident of 33 Praterstrasse, Vienna, Austria, have invented new and useful Improvements in Processes of Chrome Tanning, (for which I have filed applications in Austria, Mar. 8, 1913; in Germany, Mar. 9, 1913, Patent No. 271,585; in Hungary, Dec. 5, 1913; in France, Dec. 6, 1913, Patent No. 465,846; and in Russia, Nov. 28, 1913,) of which the following is a specification.

The object of the present invention is a process of tanning and particularly an improvement in the usual chrome tanning process, and consists in reducing the chromic acid and neutral chromic salts by a solution of bisulphite of aluminum without any further addition of an acid.

Processes are known according to which aluminum compounds are used with chromic acid or chromates.

The use of aluminum salts which have a reducing action, is mentioned for the first time in the Patent No. 528,162 which mentions thio-sulfate aluminum as a tanning substance.

The known processes generally employed thio-sulphate of soda or bi-sulfite of soda (NaHSO as a reducing agent with the' addition of an acid:

If sodium thiosulphate (Na s O is used,

velopment of heat is avoided and that the reduction of the chromic acid takes place gradually when aluminum and the like is used without the addition of an acid, while at the same time there is formed a deposit of hydrate of aluminum (Al(OH) in the hide. That is, all the advantages of tanning with basic salts, as for instance the insoluble condition of the tanning material after the conclusion of the process are derived therefrom. The bisulphites of aluminum can also be replaced by a stoechiometric mixture of bisulphite of soda and a neutral or even a basic aluminum salt.

if, instead of the bi-sulfite of soda a mixture of monoand bisodium hyposulphite is used, the composition of the deposit of chromium and aluminum oxides can be correspondingly varied.

Instead of aluminum bisulphite zinc bisulphite may be used when desired, and the retarding reaction which these two compounds can eii ect in the reduction of the chromic acid or its salts can be governed at will by the addition either of acid or of bisulphites of the alkaline earths.

What I claim is:

1. A process of chromic tanning consisting in subjecting the hides to a treatment with chromic acid and reducing the latter by stoichiometric mixture of bisulphite of soda, and a neutral salt of aluminum.

2. A process of chromic tanning consisting? in subjecting the hides to a treatment with chromic acid and reducing the latter by stoichiometric mixture of bisulfite of soda and a basic salt of aluminum.

3. A process of chromic tanning consisting in subjecting the hides to a treatment with chromic acid and reducing the latter by stoichiometric mixture of bisulfite and sulfite of soda and a neutral salt of aluminum.

In testimony whereof I aflix my signature in presence of two witnesses.

FRIEDRICH HIRSCH.

Witnesses IGNAZ KNIORFELNAOHL, RUDOLF Rrrrnn. 

